X-C motif chemokine 1 (XCL1) is a 93 amino acid XC chemokine that is chemotactic for lymphocytes but not for monocytes or neutrophils. It is also known as lymphotactin or single c motif 1 (SCM-1) and is closely related to its paralog XCL2 or SCM-1-beta. XCL1 interconverts between monomeric and dimeric forms under physiological conditions. XCL1 monomer is a ligand for the G protein coupled receptor XCR1 while the XCL1 dimer has decreased binding affinity. XCL1 is expressed at high levels in the spleen, moderate levels in peripheral leukocytes and at low levels in the lung, colon and small intestine. Cytokines are a family of secreted proteins involved in immunoregulatory and inflammatory processes. The XC chemokines are a two member subfamily of chemotactic cytokines that induce directed chemotaxis in nearby responsive cells and retain only two of the four cysteines characteristically conserved in chemokines. Recombinant human XCL1 from Molecular Innovations is provided as a native untagged protein. This chemokine is expressed in E. coli then processed, refolded and purified to yield the native, secreted form of the mature chemokine. >98percent pure by SDS-PAGE, HPLC, MALDI-MS and NMR analysis. XCR1 activity verified by intracellular calcium flux using HEK 293 cells. Add deionized water to desired volume, aliquot and freeze unused portion.